This invention generally relates to a bonding tools used for fine wire bonding, and more particularly to a capillary bonding tool having a polymer coating disposed over the surface of the capillary.
Wire bonding is, at this time, the dominant method used for the interconnection of semiconductor-based devices. In the wire bonding industry, tool failure leads to the destruction of the semiconductor device being interconnected, which can significantly lower yields. To prevent tool failures, tools are exchanged regularly prior to the predicted time of failure.
The wire bonding process is defined by the xe2x80x9cProcess Window,xe2x80x9d which is the range of parameters that the bonding machine is qualified to operate within. To maintain bond quality, adjustments must be made to the bonding parameters. Bonding parameters, however, are not allowed to be outside of the approved process window. This leads to a loss of productivity as the bonding process must be stopped and tools exchanged. Furthermore, additional expense is incurred as a larger number of tools than necessary are used.
Contamination build-up and accelerated wear limit the useable time for conventional ceramic-based tools (e.g. Alumina, Zirconia toughened Alumina, Zirconia, cemented Tungsten Carbide, etc.) in wire bonding applications. Adhesion of organic-derived carbonaceous material and the subsequent embedding in the carbonaceous material of metallic particles from the bonding wire causes unsymmetrical loading of the tool and eventually leads to mechanical failure of the bonding tool by flexural bending. The carbonaceous material is produced by the action of the Electric Flame Off (EFO, for ball formation) on the petroleum and stearate-based materials typically placed on the wire surface to improve de-spooling of the wire. Enhanced surface wear is also caused due to the localization of bonding forces to a point load on the tool face.
U.S. Pat. Nos. 5,871,141, 5,558,270, and 5,421,503 assigned to the same assignee as the present invention, describe various conventional bonding tools for producing wire bonds on semiconductor devices and are incorporated herein by reference.
In view of the shortcomings of the prior art, the present invention relates to a bonding tool having an orifice extending along a longitudinal axis of the tool body, a working tip coupled to one end of the tool body, and a polymer coating disposed over at least a portion of a surface of the orifice.
The present invention also relates to a method of manufacturing a bonding tool for bonding a fine wire to a substrate, comprising the steps of forming a cylindrical body, forming a taper at a first end of the body, forming an orifice extending along a longitudinal axis of the body, and coating the body with a polymer.
According to another aspect of the present invention, a first coating is disposed along the surface of the orifice and a second coating is disposed along an exterior surface of the bonding tool.